Electrical insulating materials for use in electric wires used in internal wiring of electronic equipment, automobiles or the like require various properties including electrical insulation properties such as dielectric strength; mechanical properties such as tensile properties, and abrasion resistance; flexibility; flame retardancy; heat resistance; cold resistance, etc.
Compositions containing vinyl chloride resins or olefin resins as main components have been used as electrical insulating materials superior in such electrical properties, mechanical properties and like properties.
However, other resins are increasingly used in recent years in place of vinyl chloride resins which raise environmental problems. Further, olefin resins are difficult to use under high temperature environments because of low heat resistance.
Attention is drawn nowadays to thermoplastic polyesters having high heat resistance and recyclability as an electrical insulating material, beside that the resin is thermoplastic. Among them, thermoplastic polyester elastomers having high elastomeric properties are widely used as a wire-coating material for its flexibility.
Among them, a polymer produced by reacting an aromatic polyester with a lactone is suitable for use under a high temperature environment such as an automobile engine room because of its high heat resistance. Especially a thermoplastic polyester elastomer containing 20 to 40% by weight of a polylactone segment has flexibility suitable as a wire-coating material.
Known methods of producing polymers by reacting an aromatic polyester with a lactone include a method comprising reacting a crystalline aromatic polyester with a lactone (Japanese Publication of Examined Application No. 4116/1973), a method comprising reacting a crystalline aromatic polyester with a lactone and reacting the obtained block initial copolymer with a polyfunctional acylating agent to give a chain extension (Japanese Publication of Examined Application No. 4115/1973), and a method comprising polymerizing a lactone in a state of solid phase in the presence of a crystalline aromatic polyester (Japanese Publication of Examined Application No. 49037/1977), etc.
Electric wires formed using the polymer obtained by these methods as an electrical insulating material have a drawback of becoming locally degraded and of losing the electrical insulating properties when subjected to water resistance and dielectric breakdown test called “Hot Water Resistance Test” among the test methods according to SAE J1678. This phenomenon is likely to occur especially when an electrical insulating layer is thin and an electric wire is connected to the anode of direct current power source. For this reason, it is difficult to commercially use these polymers as an electrical insulating material, e.g. for electric wires under an environment in which the polymer is affected by water.
Further, the foregoing shaped body when actually used may be fastened with a screw, bolt, nut, adhesive, tape, cord, film, hook or the like in order to position the shaped body according to the purpose, or to prevent contact with other material or to inhibit dispersing.
When the shaped body is fastened, problems would be posed. The degradation of shaped body may be promoted under an influence of environmental conditions (temperature, humidity) depending on a combination of a material for a fastening member with a material for a shaped body. For example, the physical strength may be markedly reduced at a portion of the shaped body in contact with the fastening member. Especially the degradation problem becomes noticeable at a high temperature exceeding 80° C. and a high humidity in the equipment or apparatus even when no problem may be raised under an ordinary environment. Such shaped body can not be used under severe conditions.